As the demand grows for higher throughput, i.e., higher bit rate, and more efficient transmission of packet data over wireless networks, the 3rd Generation Partnership Project (3GPP) has extended its specifications with the High Speed Downlink Packet Access (HSDPA) for transfer of packetized data in the downlink direction—from the radio network controller (RNC) to the radio base station (Node-B) and eventually to the user equipment (UE). HSDPA's main goal is to enhance network capacity through increased accessibility, increased throughput, and reduced latency in the downlink direction.
In the uplink direction—from the UE to the Node-B, the 3GPP has also extended its specifications with Enhanced Uplink (EUL). EUL provides features that make it faster than earlier uplink operations such as those in Release '99. The new features include multi-code transmission, short transmission time interval (TTI), fast hybrid automatic repeat request (HARQ), and fast scheduling.
FIG. 1 illustrates an example UTRAN system 100. The system 100 includes an RNC 110 communicating with the core network (not illustrated) over an Iu interface. The system also includes multiple Node-Bs 120 connected to the RNC 110 over Iub interfaces. The user equipments (UE) 130, typically mobile terminals, communicate with one or more Node-Bs 120 over a Uu interface (radio link).
The protocol layers and the nodes involved in data exchange between the RNC and the UE are illustrated in FIG. 2. The RLC (radio link control) layer of the RNC provides RLC protocol data units (PDU) to the peer RLC layer in the UE in the downlink direction. Conversely, in the uplink direction, the RLC layer in the UE sends RLC PDUs to the RLC layer in the UE. The RLC PDUs are packaged in Medium Access Control-d (MAC-d) PDUs, and these MAC-d PDUs are exchanged between the RNC and the UE through the Node-B.
Data transmission bottlenecks can occur in both the uplink and the downlink directions. The bottlenecks can also occur on the Iub interface between the Node-B and the RNC and on the Uu interface between the Node-B and the UE. Flow control is needed to handle the congestion situations.
For the uplink, the frame work for EUL Flow Control (FC) is standardized in 3GPP. In the document 3GPP TS 25.427 V6.6.0 (2006-03), “UTRAN Iub/Iur interface user plane protocol for DCH data streams”, the E-DCH (enhanced dedicated transport channel) DATA FRAME (DF) and the TNL Congestion Indication (TCI) Control Frame (CF) are defined. Based on the E-DCH DATA FRAME sequence received from the Node-B, the RNC can detect TNL (transport network layer) congestion and can indicate different type of congestions to the RBS using the TCI CF. On a transport bearer carrying an E-DCH MAC-d flow, the RNC can detect a congestion situation occurring on the Iub interface. Upon detection of the congestion situation, the RNC can notify the Node-B of the congestion through the TCI CF.
Upon reception of the TCI CF, the Node-B reduces the bit rate on the Iub interface for the E-DCH MAC-d flow. Practically, when there is congestion in the uplink of the MAC-d flow, the existing Uu scheduler controls the bit rate to resolve the congestion. Bit rate control can lead to long reaction times to changing congestion conditions, which can lead to increased latency.